Method for depositing a flattened droplet on a surface and apparatus therefor, and a pump therefor

ABSTRACT

A method and apparatus is provided for depositing a flattened droplet on a surface. The method includes the steps of providing a tube with a distal end that contains a microvolume of liquid, issuing an outgoing flow of displacement gas for slowly discharging substantially the entire microvolume of liquid as a droplet on the surface, and controllably blowing one or more bubbles into the droplet for flattening the droplet on the surface.

FIELD OF THE INVENTION

The invention relates to a method for depositing a flattened droplet ona surface suitable for in vitro fertilization (IVF) and embryo transfer(ET), and apparatus therefore, and a pump therefor.

BACKGROUND OF THE INVENTION

In an IVF-ET procedure, oocytes are aspirated from female ovaries andinseminated in vitro with male sperm in a culture medium to form embryoswhich are incubated prior to their being transferred to a subject bymeans of a two-stage transfer procedure. The transfer procedure includesthe aspiration of a relatively large volume of about 20-40 μl of culturemedium containing between one to five embryos into a transfer catheterby means of a manually operated syringe and its subsequent injectioninto a subject.

Since a conventional IVF-ET procedure is manual, the rate of injectionof the embryo containing culture into a uterine cavity may varysignificantly. Thus, on the one hand, too slow an injection rate maycause embryo containing culture medium to trickle down the transfercatheter's outer surface and, on the other hand, too quick an injectionrate may severely damage embryo(s) following their collision against auterine wall. The latter case may also flood a subject's uterus possiblyresulting in a failed procedure as embryos are either washed out of heruterus or implanted in one of her Fallopian tubes leading to an ectopicpregnancy. Another disadvantage attendant with the use of a relativelylarge volume of culture medium is that it may alter the specificproperties of the micro-environment within a subject's uterus requiredfor successful embryo implantation and its normal development.

The present invention is based on the notion that substantiallyautomating embryo implantation in IVF-ET procedures may overcome some ofthe shortcomings of the conventional IVF-ET procedure.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a method fordepositing a flattened droplet on a surface particularly suitable fordepositing embryo(s) containing culture medium at a desired site in auterus cavity, and apparatus therefor, and a pump therefor.

In accordance with a first aspect of the invention, there is provided amethod for depositing a flattened droplet on a partially absorbentsurface, the method comprising the steps of:

(a) providing a narrow bore transfer tube having a proximal end and adistal end and containing a microvolume of liquid, the proximal endconnected to a pneumatic system for issuing an outgoing flow ofdisplacement gas into the transfer tube and drawing an incoming flow ofdisplacement gas thereinto from the transfer tube; and

(b) issuing an outgoing flow of displacement gas for slowly dischargingsubstantially the entire microvolume of liquid as a droplet on thesurface-and controllably blowing one or more bubbles into the droplettowards the end of its discharge to flatten the droplet on the surface.

A “flattened droplet” in the context of the present invention can bedemonstrated on standard 80 gram/m² A4 paper for use with ink jetprinters, such paper constituting a partially absorbent surface on whicha flattened droplet of the present invention has a projected surfacearea about three to six times larger than that of a naturally formingdome-like droplet. A “partially absorbent surface” in the context of thepresent invention is one which absorbs a relatively insignificant volumeof a naturally forming dome-like droplet over about 60 seconds. Theflattening of a droplet as achieved by the method of the presentinvention is not by the relatively slow process of its being absorbedassuming it does not dry but rather as a consequence of its beingeffectively inflated by one or more bubbles of displacement gascontrollably blown thereinto towards the end of its discharge whichtypically occurs over 5-20 seconds from an initial outward displacementof the microvolume of liquid. The surface may be flat, inclined or eveninverted and still maintain the droplet in its flattened shape by virtueof the prevailing surface tension therewith.

A “microvolume of liquid” in the context of the present invention is avolume of liquid in the microliter range, e.g., within the range of0.05-5 μl, preferably within the range of 0.1-3.0 μl, and particularlywithin the range of 0.3-2.0 μl. In the case of an IVF-ET procedure on ahuman subject when the catheter is upwardly inclined, even though thedischarge of culture medium is relatively slow, its volume is so smallso as to avoid a downward trickle along the catheter's outer surface.

In accordance with a preferred embodiment of the present invention, step(a) includes:

(a1) preventing capillary forces to draw liquid into the transfer tubeupon insertion of its distal end into a vessel containing liquid;

(a2) inserting the transfer tube's distal end into the liquid;

(a3) drawing an incoming flow of displacement gas from the transfer tubesuch that a microvolume of liquid is drawn thereinto; and

(a4) removing the transfer tube's distal end from the liquid.

The step of preventing capillary forces is preferably achieved byissuing an outgoing flow of displacement gas into the transfer tube soas to create a positive pressure therein. Alternatively, this step canbe achieved, for example, by providing a seal at its distal end. Afterthe transfer tube's distal end is removed from the liquid, themicrovolume of liquid is preferably inwardly drawn away from its distalend as a safety precaution whereafter the inward displacement isneutralized by a brief outgoing flow of displacement gas into thetransfer tube.

After the discharge of the microvolume of liquid from the transfer tube,the flattened droplet in most cases is still connected to the transfertube's distal end and therefore to prevent its suction back into thetransfer tube, the outgoing flow of displacement gas is maintained untilthe droplet is disconnected from the transfer tube's distal end bymanually withdrawing the transfer tube. This outgoing flow ofdisplacement gas may also remove any small quantities of the microvolumewhich were not initially discharged and which may include an embryo(s)in an IVF-ET procedure.

In accordance with a second aspect of the present invention, there isprovided apparatus for depositing a flattened droplet of liquid on apartially absorbent surface, the apparatus for use with a narrow boretransfer tube having a proximal end and a distal end and a vessel ofliquid, the apparatus comprising:

(a) a pneumatic system connected to the transfer tube's proximal end andadapted for issuing an outgoing flow of displacement gas into saidtransfer tube and drawing an incoming flow of displacement gas thereintofrom said transfer tube; and

(b) a control mechanism for controlling said pneumatic system indifferent operational modes including:

a user controlled suction mode for drawing an incoming flow ofdisplacement gas from the transfer tube whereby a microvolume of liquidis drawn thereinto prior to the removal of said distal end from thevessel; and

a user initiated automated delivery mode for issuing an outgoing flow ofdisplacement gas into the transfer tube for slowly dischargingsubstantially the entire microvolume of liquid as a droplet on thesurface and controllably blowing one or more bubbles into the droplettowards the end of its discharge to flatten the droplet on the surface.

In accordance with a third aspect of the present invention, there isprovided a pump comprising a housing having a bore with an internalperipheral surface, and a stationary annular sealing member integrallyformed therewith at a first end of a pair of opposite ends; a slide roddisposed in said bore and having an external peripheral surface and adisplacement annular sealing member integrally formed therewith; saidsealing members sealing said peripheral surfaces to define a venteddisplacement volume therebetween whose volume is proportional to anannular cross section area between said peripheral surfaces and adistance between said sealing members; and said slide rod being slidablyreciprocable between first and second positions respectively toward andaway from said stationary sealing member whereupon said displaceablesealing member moves to reduce said volume to issue an outgoing flow ofdisplacement gas from said displacement volume on a downstroke of saidslide rod from said second position to said first position and saiddisplaceable sealing member moves to increase said volume to draw anincoming flow of displacement gas into said displacement volume on anupstroke of said slide rod from said first position to said secondposition.

Preferably both the bore and the slide rod are of a right cylindricalshape such that the displacement volume has a cross sectional areadefined by π(a²-a²) where a and b are the radii of the bore's internalperipheral surface and the slide rod's external peripheral surface,respectively. Preferably, the cross section area is in the order of 4-10mm² and the pump has a displacement volume incrementally changeable inthe order of 0.1-0.4 μl.

DETAILED DESCRIPTION OF THE DRAWINGS

With reference now to FIGS. 1 and 2, apparatus 1 is employed fordepositing a flattened droplet F on a partially absorbent surface S, forexample, on a subject's endometrium in an IVF-ET procedure. Apparatus 1includes a suction control unit 2 normally permanent located in alaboratory for the preparation of an embryo carrying catheter 3constituting a transfer tube, a transfer control unit 4 normallypermanently located in treatment room where an IVF-ET procedure iscarried out and a portable casing 6 for consecutive connection to thesuction control unit 2 and the transfer control unit 4 by means ofconnectors 7 and 8. The casing 6 includes a pneumatic system 9 which ispermanently connected to the catheter 3 during an entire IVF-ETprocedure via suitable air tubing 11 and an air filter 12. The casing 6also has a receptacle 13 for accommodating the catheter 3 during itstransport from the laboratory to the treatment room.

The pneumatic system 9 is under a control mechanism 14 including acomputer mouse 16 for controlling the suction control unit 2 forinitiating a user controlled suction mode to prepare the catheter 3 witha microvolume of embryo containing culture medium and a foot pedal 17for controlling the transfer control unit 4 for initiating a userinitiated automated delivery mode for depositing the flattened droplet Fon the surface S. The computer mouse 16 has an upstroke control 18 fordrawing an incoming flow of displacement gas into the pneumatic system 9from the catheter 3, a downstroke control 19 for issuing an outgoingflow of displacement gas from the pneumatic system 9 into the catheter 3and optionally a speed control 21 for controlling he flow rate of thedisplacement gas either from or into the pneumatic system 9. The suctioncontrol unit 2 is also provided with a reset button 22 for priming thepneumatic system 9 for a pre-suction mode of issuing an outgoing flow ofdisplacement gas as indicated by a READY indicator light 23 prior to thepreparation of the catheter 3. The different stages of the automaticdelivery mode are indicated by a READY indicator light 24, a GOindicator light 26 and a DONE indicator light 27.

In operation, the casing 6 is initially connected to the suction controlunit 2 and the catheter 3 is connected to the pneumatic system 9 via theair tubing 11 and the filter 12. An operator presses the reset button 22whereupon a lit READY indicator light 23 indicates an outgoing flow ofdisplacement gas creating a positive pressure within catheter 3 toprevent capillary forces drawing culture medium thereinto upon insertionof its distal end 3A into a vessel of culture medium C containingembryos E shown exaggerated in all FIGS. 2A-2L (see FIG. 2A). Theoperator inserts the distal end 3A into the vessel of culture medium Cfor aspirating about 0.3 to 0.6 μl microvolume of culture mediumcontaining an embryo E into the catheter 3 (see FIG. 2B). Once an embryois clearly seen to be close to the catheter's distal end 3A, the rate ofaspiration of culture medium may be increased by depressing the speedcontrol 21. IF a single embryo is to be transferred, distal end 3A isthen be removed from the culture medium otherwise additional embryos maybe captured as shown.

Once the catheter 3 contains one or more embryos, the operator withdrawsits distal end 3A from the culture medium and the proceeds to depressthe downstroke control 19 to slowly displace the microvolume of culturemedium inwardly (see FIG. 2C). After the microvolume of culture mediumhas been inwardly displaced by about 5-15 mm from the catheter's distalend 3A, its motion is arrested by a momentary outgoing flow ofdisplacement gas (see FIG. 2D) so that it finally comes to rest at adistance of about 10 mm (see FIG. 2E) therefrom thereby ensuring that itcannot be inadvertently lost during transportation of the casing 6between the laboratory and the treatment room. The catheter 3 is thenplaced in the receptacle 13 (see FIG. 1) during the transportation ofthe casing 6 from the laboratory to the treatment room.

For transfer of the embryos E onto the surface S, the catheter 3 is laidon the surface S (see FIG. 2F) whereupon a first depression on the footpedal 17 causes the READY indicator light 24 to be lit indicating thatthe automatic delivery mode can be initiated. Thereafter, a seconddepression on the foot pedal 17 causes the GO indicator light 26 to belit indicating that an outgoing flow of displacement gas is displacingthe microvolume of culture medium towards the catheter's distal end 3A(see FIG. 2G). The outgoing flow of displacement gas causes a concaveshaped meniscus to be slowly formed which increases in size until itsuddenly ruptures whereby most of the microvolume of culture medium isdischarged as a droplet D on the surface S (see FIGS. 2H and 2J). Thedischarge is accompanied by one or more air bubbles B for effectivelyinflating the droplet D thereby considerably widening its projectedsurface area on the surface S to form the flattened droplet F whoseshape is maintained by its prevailing surface tension with the surface S(see FIG. 2K).

The GO indicator light 26 is then extinguished indicating that theoperator should slightly withdraw the catheter 3 so as to detach it fromthe droplet F whilst at the same time there is an outgoing flow ofdisplacement gas (see FIG. 2L). In the case of an actual IVF-ETprocedure, withdrawal is limited to between about 10-15 mm such that thecatheter's distal end 3A still lies along a subject's endometrium.Finally, a further outgoing flow of additional displacement gas isprovided so as to remove any culture medium which may remain in thecatheter 3. The DONE indicator light 27 is then lit to indicate that thecatheter 3 can be completely removed.

With reference now to FIGS. 3-5, a pump 31 constituting a pneumaticsystem for use with the apparatus 1 includes a base 32 with a housing 33having a longitudinal right cylindrical throughbore 34 with an internalperipheral surface 36 of a radius a and having first and second oppositeends 37 and 38. A right cylindrical slide rod 39 with an externalperipheral surface 41 of a radius b and first and second opposite end 42and 43 is disposed in the bore 34 and is slidingly reciprocated by meansof a linear actuator screw 44 driven by a step motor 46.

A sleeve bearing 47 having a sealing O-ring gasket 48 constituting astationary annular sealing member is disposed at the first end 37 and anO-ring gasket 49 constituting a displaceable annular sealing member isdisposed at the slide rod end 42, the gaskets 48 and 49 sealingly theperipheral surfaces 36 and 41 to define a displacement volume 51 ventedby a vent 52. The displacement volume 51 has a volume equal to a productof a cross sectional area between the surfaces 36 and 41 defined byπ(a²-b²) and the distance between the gaskets 48 and 19.

The slide rod 39 is slidingly reciprocable between first and secondpositions respectively toward and away from the gasket 48 whereupon thedisplacement volume 51 has a minimum value when the gaskets 48 and 49are adjacent in which case a major portion of the slide rod 39 isexterior to the bore 34 and a maximum value when the gaskets 48 and 49are remote from one another. In operation, the gasket 49 moves to reducethe volume of the displacement volume 51 to issue an outgoing flow ofdisplacement gas therefrom on a downstroke of the slide rod 39 from itssecond position to its first position and the gasket 49 moves toincrease the volume of the displacement volume 51 to draw an incomingflow of displacement gas thereinto on an upstroke of the slide rod 39from its first position to its second position.

The bore 34 and the slide rod 39 typically have diameters in the rangeof about 5-10 mm and which differ in the range of about 0.3-0.7 mm suchthat the cross section area is in the order of about 4-10 mm². Thethreading on actuator screw 44 is designed such that each step of themotor 46 causes an incremental movement of the slide rod 39 of about0.001-0.002 inches. The motor 46 is typically driven at a rate of about20-300 steps per second.

Various modifications and changes may be made in the configurationdescribed above that come within the spirit of the invention. Theinvention enbraces all such changes and modifications coming within thescope of the appended claims.

What is claimed is:
 1. A method for depositing a flattened droplet on apartially absorbent surface comprising the steps of: (a) providing anarrow bore transfer tube having a proximal end and a distal end andcontaining a microvolume of liquid, the proximal end connected to apneumatic system adapted for issuing an outgoing flow of displacementgas into the tube and drawing an incoming flow of displacement gastherefrom; and (b) issuing an outgoing flow of displacement gas forslowly discharging substantially the entire microvolume of liquid as adroplet on the surface and controllably blowing one or more bubbles intothe droplet towards the end of its discharge for flattening the dropleton the surface.
 2. The method of claim 1 wherein step (a) includes: (a1)preventing capillary forces from drawing liquid into the transfer tubeupon the insertion of its distal end into a vessel containing liquid;(a2) inserting the transfer tube's distal end into the vessel; (a3)drawing an incoming flow of displacement gas from the transfer tube suchthat a microvolume of liquid is drawn thereinto; and (a4) removing thetransfer tube's distal end from the liquid.
 3. The method of claim 2wherein step (a1) includes issuing an outgoing flow of displacement gasinto the transfer tube.
 4. The method of claim 3 further comprising thestep of: (a5) drawing the microvolume of liquid into the transfer tubeaway from its distal end; and (a6) neutralizing the inward displacementby a brief outgoing flow of displacement gas into the transfer tube. 5.The method according to claim 1 further comprising the step of: (c)providing an additional outflow of displacement gas while displacing thetransfer tube away from the droplet so separate the droplet from itsdistal end.
 6. The method according to claim 1 wherein the microvolumeof liquid is a culture medium containing embryo(s) which are urgedagainst the surface by the droplet's prevailing surface tension. 7.Apparatus for depositing a flattened droplet on a partially absorbentsurface, the apparatus for use with a narrow bore transfer tube having aproximal end and a distal end and a vessel of liquid, the apparatuscomprising: (a) a pneumatic system connected to the transfer tube'sproximal end and adapted for issuing an outgoing flow of displacementgas into said transfer tube and drawing an incoming flow of displacementgas thereinto from said transfer tube; and (b) a control mechanism forcontrolling said pneumatic system in different operational modesincluding: an user controlled suction mode for drawing an incoming flowof displacement gas from said transfer tube whereby a microvolume ofliquid is drawn thereinto prior to the removal of said distal end fromthe vessel; and an user initiated automated delivery mode for issuing anoutgoing flow of displacement gas into said transfer tube for slowlydischarging substantially the entire microvolume of liquid as a dropleton the surface and controllably blowing one or more bubbles into thedroplet towards the end of its discharge for flattening the droplet onthe surface.
 8. Apparatus according to claim 7 wherein said controlmechanism includes an automatic pre-suction mode for issuing an outgoingflow of displacement gas.
 9. Apparatus according to claim 1 claim 7wherein separate units house a suction control unit for controlling saiduser controlled suction mode and a transfer control unit for controllingsaid user initiated automatic delivery mode.